Method of converting hydrocarbon oil



Dec. 28, 1937.- H. A. SMITH 2,103,561

METHOD OF CONVERTING HYDROCARBON OIL- I Filed Aug. 25, 1952 HEFLUX MIN COIYDE/BE/P Flex.

(ll/WE LEVEL REACT/0N VESSEL HEIGHT/01V VESSEL I'M/IV cows/van? F I62. 3W a. W

INVENTOR 19M 13 ATTORNEY Patented Dec. 28, 1937 METHOD OF CONVERTING HYDROCARBON OIL Harris A. Smith, Port Arthur, Tex, assignor to The Texas Company, New York, N. 'Y., a corporation of Delaware Application August 23,

4 Claims.

This invention relates to the conversion of higher boiling hydrocarbon oils into lower boiling ones and relates particularly to a method of treating petroleum oil to obtain a maximum yield of motor fuel distillate having a relatively high anti-knock value.

The invention contemplates cracking preferably a viscous relatively dirty oil, such as topped or reduced petroleum, by first cracking it in the liquid phase, then cracking a separated clean gas oil fraction resulting therefrom in the vapor phase. It further contemplates recycling an equally clean reflux condensate through the vapor phase cracking zone and subjecting a residue from the liquid phase step to vaporization and the resulting vapor to a time of digestion in the vapor phase reaction chamber while discharging a final residue.

In the first or liquid phase stage of the operation the invention principally contemplates lowering or breaking the viscosity of the charge stock, without producing coke, to make the maximum percent of the original charge oil available as gas oil for the subsequent treatmentto produce a superior quality motor fuel. The treatment given the oil in the first phase usually does, however, produce a small quantity of I Inctor fuel.

In the second or vapor phase stage of cracking the invention principally contemplates subjecting the gas oil, and optionally the motor fuel fraction, which is developed in the first or liquid phase stage, to such conditions of treatment as will produce the maximum quantity of high grade motor fuel, from the standpoint of antiknock value, and leave as a residue a pitch-like substance which is suitable for use as a heavy fuel oil base. As an essential feature of this phase of treatment there is included the recycling of a reflux condensate which is separated from the overhead vapor from the vapor phase reaction chamber. As a further'feature the residue resulting from the liquid phase treatment may be subjected to appropriate conditions of partial vaporization, and the resulting vapor may be subjected to the cracking conditions of the vapor phase reaction chamber.

According to the invention a relatively viscous charge oil may be heated to an appropriate temperature and delivered into a cracking chamber wherein a body-oi the oil is maintained under suitable conditions of pressure and temperature to effect the desired conversion of it. In the chamber where soaking is effected the time is preferably reduced somewhat from that of the 1932, Serial No. 630,016

ordinary well-known liquid phase cracking process in which gasoline is produced. As the oil is also preferably heated more rapidly in the coil to the desired temperature, than it is in theordinary heater coil, thus reducing soaking in the heating stage to a minimum, the oil may be heated to a somewhat higher temperature than has been customary heretofore.

The volume of heated oil undergoing soaking,

, which may govern the time of soaking when assuming an optimum charge rate, may be regulated by systematically withdrawing a portion of the unvaporized or residual material as it accumulates in the cracking or soaking chamber. The liquid withdrawn is preferably passed into the vapor phase cracking vessel, where somewhat lower pressure and higher temperature are maintained.

Vapor developed in the liquid phase soaking chamber, which-consists mainly of gas oil constituents, is preferably scrubbed clean in the soaking chamber and is then dephlegmated to produce an overhead vapor, which is condensed as motor fuel distillate, and a clean gas oil or reflux condensate.

The clean reflux condensate dephlegmated from the liquid phase vapor is subsequently heated to a considerably higher temperature than the original charge oil was heated to, and delivered into the vapor phase reaction chamber where conditions of vapor phase cracking are maintained. The relatively heavy liquid, which is also delivered into the vapor phase reaction chamber from the liquid phase soaking chamber, may be introduced below the point of introduction of the highly heated reflux condensate, to avoid a complete heat interchange which might be deleterious to both. On the other hand the temperature of the residual material is preferably raised sufficiently to effect vaporization of the lighter portion of it at the pressure maintained and perhaps toeiiect some further decomposition of the more viscous unvaporized portion before it is discharged from the system;

Vapor developed in the vapor phase reaction chamber is preferably scrubbed clean in the reaction chamber and is then commingled with the vapor from the liquid phase soaking chamber and is dephlegmated to produce an overhead vaporous motor 1 fuel and a clean condensate which is recycled through the vapor phase crack ing zone. The gathering residual material is discharged from the system at this point practically as soon as it is deposited.

The various advantages of the invention may be better understood by referring to the accompanying drawing, illustrating preferred forms of apparatus for carrying out the process of the invention in which:

Fig. 1 is a diagrammatic view in elevation of a cracking system according to the invention Fig. 2 is a diagrammatic view in elevation of a cracking system illustrating a modification of the form shown in Fig. 1.

Referring now to Fig. 1 of the drawing:

A pump I is arranged to withdraw a suitable charge oil from storage, not shown, and deliver it through a pipe 2 and a preheater 3, through a pipe 5, into a furnace heater coil 6,

From the heater coil 6 the heated oil is delivered through a pipe I into a soaking or reaction vessel i l. Vapor produced in the soaking vessel H may be withdrawn overhead through a line l2 while a residue may be withdrawn through a line l3, having reducing valve 59, and delivered into a second reaction vessel l5 or may be discharged through a connecting line 20.

Vapor forming in the reaction vessel l5 may be withdrawn overhead through a line l6 .While residue may be withdrawn from a lower portion of the vessel I5 through a line 2| which is connected to a discharge line 22. Appropriate valves I4, 23, and 24 are provided for directing the flow of residue from the vessel H into the vessel l5 or from either of the vessels H and l5 out of the system through the line 22.

A vapor line 25 is provided for conducting the vapor from vessels H and I5 to a dephlegmator 30. A pipe connection 3| leads from the lower portion of the dephlegmator 39 to a pump 35 which serves to withdraw condensate from the dephlegmator and discharge it through a pipe 36 into a furnace heater coil 40. The highly heated oil from the heater coil 49 is conducted through a line 4i into the lower portion of the reaction vessel IS.

A line 37 having branches 38 and 39 serves to conduct any desired portion of the condensate to the upper portions'of the vessels l5 and H, respectively, as a refluxing medium.

Vapor from the dephlegmator 30 is passed over head through a line 45 into a reflux condenser 46, in which the preheater 3 is situated. A line 4'! is provided for trapping condensate from the lower portion of the reflux condenser 46 back to the dephlegmator 3!) while vapor from the reflux condenser 46 is passed overhead through a line 48 and is condensed in a main condenser 49 to be delivered through a line 50 to storage. The function of pipe line I! will be explained more fully hereinafter.

In a preferred mode of operation a fresh charge oil, which may be a topped. or reduced petroleum, for example that produced by reducing 3436 A. P. I. gravity M. C. crude, to 24-26, is preheated in the coil 3 and is finally heated in the coil 6, to an appropriate cracking temperature, which may be of the order of 800 F. to 850 F. It is then delivered under a superatmospheric pressure of say 490 lbs. per square inch into'the soaking and vaporizing vessel H. Vapor forming in the vessel is withdrawn overhead and passed to the dephlegmator 30 while a remaining residual material may be delivered into the reaction vessel i5, in which a lower pressure is maintained, say about 300 lbs. per square inch and wherein additional vaporization is eifected. The vapor from each of the vessels H and i5 is preferably scrubbed in the vessel in which it is formed to remove all cokey and tarry constituents, and is delivered to the dephlagmator 30, the vapor from vessel H passing through reducing valve 51.

Dephlegmated vapor is withdrawn overhead from the dephlegmator and condensed as a motor fuel distillate and a clean reflux condensate is removed from the lower portion of the dephlegmator and passed through the second heater coil 40. The clean condensate is heated in the coil 40 to a temperature of say 950 E, which is considerably higher than that to which the original charge oil was heated. This highly heated oil is then delivered into the vessel l5 where the evolving vapor is subjected to a time of digestion, along with the vvapor evolving from the residue, which is discharged into this vessel from the vessel H, while the unvaporized residue is discharged from the system as soon as it is deposited in the lower portion of the vessel.

The volume of liquid in the vessel Il may be regulated according to the length of time necessary to effect the desired amount of conversion but usually it will be of about half of the capacity, or slightly more, of the vessel l I. It is preferable to effect this liquid phase of conversion at as high a temperature as is practicable, because the time of soaking may be decreased as the temperature is increased, and superior anti-knock motor fuels are produced at the higher temperature. However, as the primary purpose of this phase of the operation is to reduce the viscosity of the charge oil to thereby make a maximum percent of it available in the form of gas oil for conversion at a higher temperature, the invention does not contemplate establishing such cracking conditions in this phase as to produce a substantial quantity of motor fuel. Consequently it is preferable to regulate the degree of heating and the time of soaking to effect maximum reduction of viscosity with minimum formation of coke. As it is contemplated, however, that some gasoline constituents will be formed in this stage, it is desirable to operate at the highest practical temperature to produce as high grade motor fuel as possible.

The stream of residue from the first vessel H,.

entering the vessel l5, receives some additional heat from the stream of more highly heated reflux condensate and, due also to the reduced pressure, a substantial quantity of the lighter portion of it is flashed into vapor. Such constituents of both streams as remain unvaporized in the vessel l5, which are preferably only those of a tarry or pitch-like character, are discharged from the lower portion of the vessel I5 almost as soon as deposited there, only enough of the residue being accumulated to maintain a liquid seal in the bottom of the vessel.

In order to effect the scrubbing action or cleansing of the vapor in the upper portion of the vessels H and I5, as previously referred to, it may be preferable to provide bafile arrange ments such as plates 50 and 5! respectively, in them, and to divert small streams of relatively cool condensate from the bottom of the dephlegmator through the pipe 31 having branches 38 and 39 thereto. If this material is not cool enough it may be passed through a cooling coil (not shown) prior to delivery into these vessels.

The vapor from the vessels It and I5 is preferably commingled and delivered to the dephlegmator 36, it being understood that the vapor from the vessel 1 I may consist preponderantly of gas oil constituents while the vapor from the vessel I5 may include a substantial percent of gasoline constituents.

mingled with the vapor from the vessel l just,

prior to entering the dephlegmator, the remainder passing directly to the heater 4!}, while the gasoline constituents are mixed with the clean gas oil charge just prior to its entry into the heater 4B. In this manner the gasoline constituents may be subjected to reforming to improve their anti-knock value, and portions of the clean gas oil constituents may be used as a reflux or a direct cooling agent, and all of it may be eventually subjected to the vapor phase cracking conditions previously described, which are more favorable to converting it into superior quality motor fuel.

Referring to Fig. 2 a branch line 26 is provided for conducting the vapor from the vessel H through a partial condenser 21 in which the gas oil constituents are condensed out. All of the products are then moved through a separator 28 from which the gas oil condensate is conducted proportionally to the upper portions of the vessels H and I5, being passed through a line 31 and delivered to the vessels by the lines 39 and 38 respectively, and through line 29 to the dephlegmator 30, as a reflux medium. In case additional condensate is available in excess of that necessary for cooling or refluxing, the remaining portion may be drawn direct into the suction line of the pump 35through a line 44. The proportioning of the flow of the gas oil condensate may be regulated as desired by valves 52, 53, 55 and 56.

The vaporous gasoline constituents are withdrawn overhead from the separator 28 and passed through the condenser 42 into a; gas separator 43, from which they are pumped as a liquid into the line 36, which conducts recycle condensate from the dephlegmator 30 to the heater coil 4|].

As a further alternative, which however will not in most cases be quite as beneficial to the gasoline constituents developed in the liquid phase, as that just described, butwill serve to improve the anti-knock quality thereof, the entire vapor stream from the vessel H may be passed through a line H, having reducing valve 58, shown in Figgl of the drawing, to commingle with the highly heated oil from the heater coil All before it is delivered into the vessel I5. In

case thismode is used it may be preferable to heat the oil in the coil M1 to approximately 975 F. or 1000 F. at its outlet.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limita tions should be imposed as are indicated in the appended claims.

I claim:

1. The process of producing gasoline from relatively heavy hydrocarbon oil which comprises heating said heavy oil to a cracking temperature under superatmospheric pressure, to cause mild cracking thereof in the liquid phase, separating the resulting cracked products into vapors and a liquid residue, introducing said vapors into a partial condensing zone wherein the heavier fractions thereof are condensed, introducing a portion of the condensate so formed into an upper point in a separate reaction zone, introducing said liquid residue into said reaction zone, introducing hot cracked vapors into said reaction zone to maintain the temperature thereof at a cracking value, removing cracked vapors from said reaction zone and introducing them into a dephlegmating zone wherein separation therecf into a clean condensate and a vapor fraction of desired boiling characteristics takes place, introducing another portion of said condensate first mentioned into said dephlegmating zone, re'moving uncondensed vapors from said partial condensing zone, condensing the removed vapors and heating the condensate so formed, in mixture with said clean condensate and a portion of said condensate first mentioned, to a vapor phase cracking temperature, to form said hot cracked vapors, and withdrawing unvaporized residue from said reaction zone at such a rate as to prevent the accumulation of large amounts of liquid therein.

2. The process of producing relatively high anti-knock gasoline from heavier hydrocarbons which comprises passing relatively heavy hydrocarbon oil charging stock through a once-through cracking zone, through which no product of the process is cycled, wherein the heavy oil is raised to a liquid phase cracking temperature, introducing the resulting heated products into a first reaction zone wherein a high liquid level is maintained and wherein cracking of the hydrocarbon oil in the liquid phase takes place, separately removing vapors and liquids from said reaction zone, passing said vapors to a first 'fractioriating zone wherein gasoline constituents are separated as vapors from a heavier fraction as reflux condensate, removing the gasoline constituents, mingling them with a clean gas oil cracking stock, heating the resulting mixture to a vapor phase cracking temperature in a heating zone, introducing the resulting heated products intoa second reaction zone, passing vapors from said second reaction zone to a second fractionating zone to cause fractional condensation thereof, removing at such a rate as to prevent the accumulation therein of any considerable quantity of liquid oil,

whereby cracking in said second mentioned reaction zone is carried out substantially in the vapor phase.

3. The process of converting high boiling hydrocarbon oil into lower boiling products which comprises heating the high boiling oil to a liquid phase cracking temperature, maintaining a mate rial body of resulting'hot liquid in a cracking zone maintained at a cracking temperature under superatmospheric pressure to effect cracking in the liquid phase and wherein separation into vapors and liquid residue takes place, passing the separated vapors into a subsequent cracking zone, fractionating vapors evolved in the subsequent cracking zone to separate out a light distil late and a heavier condensate, passing said heavier condensate through a vapor phase heating zone wherein it is subjected to a vapor phase cracking temperature, introducing the resultant cracked products from the vapor phase heating zone into said subsequent cracking zone to maintain the temperature therein at a cracking value and withdrawing liquid therefrom at a rate adequate to prevent the accumulation of liquid therein while maintaining a mass of vapors therein undergoing cracking in the vapor phase.

4. The process of converting high boiling hydrocarbon oil into lower boiling products which comprises heating the high boiling oil to a liquid phase cracking temperature, maintaining a material body of resulting hot liquid in a cracking zone maintained at a cracking temperature under superatmospheric pressure to eifect cracking in the liquid phase and wherein separation into vapors and liquid residue takes place, passing the separated vapors into a subsequent cracking zone,

fractionating vapors evolved in the subsequent cracking zone to separate out a light distillate and a heavier condensate, passing said heavier condensate through a vapor phase heating zone wherein it is subjected to a vapor phase cracking temperature, introducing the resultant cracked products from the vapor phase heating zone into said subsequent cracking zone to maintain the temperature therein at a cracking value and directing liquid residue from said liquid phase cracking zone into said subsequent cracking zone to thereby subject the residue to further conversion and withdrawing liquid from the subsequent cracking zone at a rate adequate to prevent the accumulation of liquid therein while maintaining a mass of vapors therein undergoing cracking in the Vapor phase.

HARRIS A. SMITH. 

